At present, tablets, laptops and other display equipments develop toward lightweight and thin. For the backlight module of display devices with small screen (below 10.1 inches), membrane material architecture without upper diffusion sheet is used to meet market demand. The periphery of the upper diffusion sheet has a printed black edge structure, which can be effectively used for avoiding light-leaking situation on the edge of the prism. When using architecture without upper diffusion sheet, in order to avoid light-leaking phenomenon on the edge, a black shading tape with a shape of a rectangle frame is typically attached on the periphery of the prism sheet to form a black peripheral zone.
Currently, the approach of attaching black shading tape with a shape of a rectangle frame has the following defects: (1) attaching the shading tape is difficult, long time consuming, with a low production rate. The scrappage of the upper prism sheet and the shading tape is large; the cost of the backlight module is high; (2) the shading tape with a shape of a rectangle frame is formed by hollowing the center part of the shading tape sheet, which will cause a large amount of waste and a high cost of materials; (3) the independent set shading tape occupies a certain thickness, increasing the thickness of the backlight module, which is contrary to the current trend of thinness.